1. Field of Application
The present invention relates to an apparatus installed on a vehicle (referred to in the following as the local vehicle) for detecting obstacles based upon the contents of captured images of a region ahead of the vehicle.
2. Related Technology
Technology is known whereby images captured as data by an electronic camera installed on a vehicle can be processed to detect the presence of a preceding vehicle or a fixed obstacle that is located ahead of the local vehicle. Such an apparatus may also be used to detect the traffic lane in which the local vehicle is running, i.e., by detecting lane markers on the road surface. Technology is also known whereby information concerning the positions of obstacles (such as other vehicles) and concerning the condition of the road (e.g., extent of curvature, slope angle, etc.) can be acquired through communication with other vehicles (this being referred to as inter-vehicle communication in the following) or with equipment that is located beside the road along which the local vehicle is travelling, and which is configured to generate and transmit such information (referred to in the following as road-to-vehicle communication).
Such acquired information can be used to define a limited-size region within a captured image obtained by the camera of the local vehicle (i.e., as a region likely to contain objects that are to be detected). By applying image processing to such a limited region, the accuracy of detection can be increased, and the processing load reduced. The above technology is described for example in Japanese patent publications No. 8-167092, and 2007-34477.
However such technology enables only a reduction of the amount of image processing required, and an increase in reliability of detecting the presence of obstacles, or detecting lane markers on the road surface, etc., and an increase in the detection speed. However in order to control a vehicle to avoid collisions with preceding vehicles, etc., and ensure safety in the event that a collision occurs, it is essential to acquire precise real-time distance and relative position information concerning obstacles that are located ahead of the local vehicle. Until now it has been necessary to utilize some separate apparatus, such as a radar apparatus, to achieve such precise measurement of positions and distances.
Another problem is that when there is a slope in the road surface ahead of the local vehicle, it becomes difficult to accurately identify obstacles (i.e., distinguish dangerous obstacles from other objects) based upon the contents of captured images. This will be described referring first to the example shown in FIG. 4(a). Here, a road surface 10 has a horizontal portion which is succeeded by an upwardly-sloping portion 11 as shown, with a road surface marker 13 (e.g., lane marker) located on the upwardly-sloping portion 11. As can be understood from FIG. 4(b), when an image containing the marker 13 is captured along the direction indicated by the arrow, i.e., by a camera of a vehicle situated on the road surface portion 10, it will not be possible to determine whether a region in the image that represents the marker 13 actually represents such a 2-dimensional object, or represents a 3-dimensional object 14 (i.e., an actual obstacle). Similarly in the example of FIG. 4(c), the road surface has a downwardly-sloping portion 12, on which an actual obstacle 15 (3-dimensional object) is located as shown. In this case, as illustrated by FIG. 4(d), it will not be possible to determine (based on image processing) whether a region in an image which represents the obstacle 15 actually represents such a 3-dimensional object, or a non-dangerous object 16 such as a road surface marker. It can thus be understood that if obstacle detection is performed simply based upon shapes and positions of regions within a captured image, reliable discrimination between actual obstacles and road surface markers, etc., cannot be achieved.